The present invention relates to a laser catheter for pinpointed application of laser light on the walls of intracorporal vessels, the laser catheter having optical fibers which are disposed ring-shaped and surround an inner hollow channel.
There are increasing possible uses of laser catheters in surgery due to the growing number of different structural designs of laser catheters and their distal end regions.
For instance, laser catheter tips are known which can, in particular, be employed in bypass surgery and which are especially distinguished by the fact that the cross section of the distal end of the laser catheter at which the light exits is completely composed of optical fibers. Such catheters are referred to, by way of illustration, as "full multifiber catheters".
With the aid of the aforementioned type of catheter, techniques for laser-aided anastomosis (surgical joining of two hollow organs, such as, attaching an additional blood-carrying channel (bypass) to a bloodchannel artery whose flow cross section is narrowed by deposits) are known, which permit bypass surgery without interrupting the blood flow in the main artery. For instance, the essays published by Rudolf Verdaasdonk et al. ("End-to-Side Anastomosis of Small Vessels Using an Nd:YAG Laser with a Hemispherical Contact Probe"; J. Neurosurg Vol. 76, March 1992; "Use of the Excimer Laser in HighFlow Bypass Surgery of the Brain", J. Neurosurg, Vol. 78, March 1993) deal with a surgical technique presenting bypass surgery in the brain with the aid of neodym-YAG or excimer lasers, without impairing the blood flow of the main blood-carrying artery affected by the surgery.
First a bypass is sewn onto the outer circumference of the artery to be treated. Through this bypass, a laser catheter tip, which is designed elastically at the distal end, is inserted and positioned within the bypass, onto the outer wall of the main artery to be treated. The laser is activated and by means of an ablation process makes a hole in the main artery (through which a part of the blood flow can be diverted) in the region of the light exit at the distal end of the optical fiber.
In addition to the great advantage of being able to conduct bypass surgery without interrupting the main artery, which is especially vital in bypass surgery in the brain, however, this known surgical technique has the drawback that the ablated material from the vessel wall resulting from-the light impingement by the laser catheter tip remains inside the blood stream and, under unfavorable circumstances may reach points in the blood stream of smaller diameter and obstruct them totally. In particular, in the brain, such tiny particles of tissue in the blood stream circulation are the cause of spontaneous strokes.
The described bypass surgery technique and the optical fiber arrangement therefor for the distal end regions of catheters, are discussed in a publication of the Medical Laser Center, Heart-Lung Institute, Department of Neurosurgery entitled "Multifiber Excimer Laser Catheter Design Strategies for Various Medical Applications" by R. Verdaasdonk et al.
The object of the present invention is to design a laser catheter for pinpointed application of laser light at the walls of intracorporal vessels, such laser catheter having optical fibers which are ring-shaped and surround an inner hollow channel, in such a manner that the risk of ablation remains obstructing blood-carrying vessels following the application of laser light is completely eliminated.
Another object of the invention is to provide a laser catheter arrangement such that the separation of the vessel wall to be treated corresponds exactly to the geometry of the tip of the laser catheter in order to permit a predefined cross section for the vessel wall penetration.
These and other objects and advantages are achieved by the present invention, which is based on the one hand on a special design of the tip of the laser catheter that makes it possible for the first time to make a geometrically exactly predefined hole in the wall of a vessel to be treated, and at the same time ensures that separated remains of the vessel wall do not stay in the blood stream, but rather are brought out of the body with the aid of the laser catheter.
For this purpose, the laser catheter according to the invention has optical fibers which are disposed in a ring-shaped configuration surrounding an inner hollow channel, and is provided at the outer circumference of its distal end with a circumference-widening element through which the optical fibers penetrate in the beam direction. With this arrangement of the optical fibers, the distal tip of the laser catheter thus assumes the form of a planar, ring-shaped light exit area.
The element widening the outer circumference of the laser catheter serves basically as a type of stop device which permits the surgeon to determine when the ring-shaped optical fibers projecting at its distal end have reached the maximal penetration depth through the region of the vessel wall which is to be ablated. The surgeon must terminate the penetration procedure at the latest when the edge of the outer circumference of the widening elements comes into contact with the outer wall of the vessel itself or with an object joined to the outer wall of the vessel. By the stop edge coming into contact with the outer wall of the vessel, the outer wall of the vessel is pressed into the same shape as the design of the stop edge, ensuring that the optical fibers rest evenly on the vessel wall.
Furthermore, the ring-shaped arrangement of the optical fibers permits separation of a circular disk of the wall vessel which is deposited inside the optical fiber arrangement. If the laser catheter is carefully extracted from the cut vessel wall, no ablation remains stay in the blood circulation system, because the circular, separated piece of vessel wall is held inside the laser catheter, by means of the low pressure prevailing therein.
The invented laser catheter is also provided with a perforated member disposed at its distal end terminating the hollow channel. The distance from the perforated member to the planar, ring-shaped light exit area of the optical fibers corresponds at least to the thickness of the to be ablated vessel wall. With such dimensioning, the elastic vessel wall is sucked to the top side of the perforated member by the low pressure prevailing inside the hollow channel, in an advantageous manner. Consequently, on the one hand, the light exit area of the optical fibers comes fully into contact with the surrounding vessel wall and, on the other hand, the vessel wall lies largely very close to the inner profile yielded by the ring-shaped optical fiber channel and the perforated member in order to ensure circular separation of the vessel wall.
Furthermore, according to the present invention, the separation procedure can be optimized by the catheter tip's engaging, during application of the laser light, with a particularly disposed ring-shaped element, on the one hand ensuring that the separation of the piece of the vessel wall occurs completely and on the other hand preventing any further injury to vessel walls, (such as to the opposite vessel wall of the blood-carrying artery). The ring-shaped element is joined to the bypass channel independent of the catheter tip in such a manner that the vessel wall is made taut during application of the laser light. Thus, the ring-shaped laser catheter tip rests evenly on the vessel wall, which is a prerequisite for a homogeneous light impingement.
The laser catheter tip according to the invention thus permits for the first time the achievement, from exterior of a vessel wall, of a controlled penetration through the vessel wall, without creating possible burnt waste products which may occur when the laser light is applied at the vessel wall, or other small pieces of vessel wall which can form for other reasons during cutting of the vessel wall. Consequently, the risk potential of blockage at distant bottlenecks in the blood stream due to burnt waste products is completely eliminated.
In an especially advantageous embodiment, if the hollow channel, which is surrounded by the ring-shaped optical fibers and is joined to a low pressure source, is provided at its distal end with a perforated member having an arrangement of concentrically disposed boreholes therein. Such boreholes perforate the member in such a manner that an even suction effect can be achieved in order to fix the separated vessel wall evenly to the surface of the perforated member, by means of the low pressure.
Other objects, advantages and novel features of the present invention will become apparent from the following detailed description of the invention when considered in conjunction with the accompanying drawings.